The present invention is relates generally to a valve for the control of flow of liquids or gases. More specifically, the present invention relates to a tubing pinch valve used to control flow through a tube where the valve is compact and durable with the capability of precise flow adjustability.
It is well known in the art to employ pinch valves or clamps to constrict the flow of a liquid or gas through a line of tubing. In particular, pinch valves are often used with flexible plastic or rubber tubing for the control of flow. Known pinch valves have the advantage that they may be free from contamination by the process fluid and that they may be used reliably with flow material containing particulate.
Pinch valves generally employ a simpler construction than other valves used to control flows. As a result, pinch valves are less costly than other known valves which require seals or the like that must resist the corrosive effects of direct exposure to the process materials such as liquids. Valves that use seals require significantly more maintenance than pinch valves and are generally of a larger size making their use more cumbersome. Another advantage of pinch valves is that they may be designed to permit installation without disconnecting the tubing line. Such a feature is critical where, in some applications, disconnection of the tubing is not possible. Also, a pinch valve may be of the on/off type only, while others provide a means to vary the flow of material through the tubing. Variation of flow may be either continuous or incremental between the fully open and fully closed positions.
For example, a known type of pinch valve, a type 25R manufactured by Research Control Valves, uses a spherical ball to compress the tubing line. The ball is pushed, not rotated, into and against the wall of the tubing. External energy is required to maintain the spherical ball in its valve position. Such an apparatus is very bulky and is not appropriate for use with smaller sized tubing. The spherical ball valve apparatus is well suited for on/off applications but since it is devoid of any calibration, it is poorly suited for incremental flow control.
Similar prior art pinch valves employ a threaded stem with a bullet nose, for contact with the tubing line, that engages with a cooperating saddle with matching threads. An important feature of pinch valves is the ability to attach to an existing tube line without disconnecting it. Many of these prior art devices employ flow control but cannot be threaded onto an existing tube run.
Examples of such pinch valves are disclosed in U.S. Pat. No. 3,848,634, U.S. Pat. No. 3,332,439, U.S. Pat. No. 2,908,476, U.S. Pat. No. 3,167,085, and U.S. Pat. No. 4,312,493.
Known types of clamps have similar disadvantages as the pinch valves described above. For example, a KECK Ramp Clamp provides no calibration and has low mechanical advantage so its application is limited to a small range of tubing wall thickness and size. A compression of the tubing is required so true full flow cannot be realized. KECK Ramp Clamps are not suitable for manufacture in materials other than plastic nor vacuum applications.
Spring tubing clamps provide no calibration and may be used for on/off control only and are not suitable for vacuum applications. Ratchet tubing clamps provide no calibration and lack fine adjustment capabilities, particularly when the tube is compressed greater than 50%. Ratchet tubing clamps have low force capability and, as a result, are limited to lighter wall thicknesses and are not suitable for vacuum applications.
Steel tube clamps do not provide calibration and, due to their design, are suitable for manufacture in metal materials only and are not appropriate for small sized tubing. Further, screw clamps also do not provide calibration and have a weak design in plastic which is the only material appropriate for this design. A wide anvil is required because the screw clamp spreads the tubing out. Such a construction creates higher stresses and limits the application in light tubing.
Although these valves provide some advantages, the need still remains for a pinch valve that can operate over a wider range of tubing flexibilities which ultimately results in a wider range of pressure and vacuum conditions. There is a need to combine those advantages with the ability to adjust and repeat valve settings with accuracy. Tubing suitable for larger vacuum lines has relatively thick walls, requiring more force to squeeze the tubing closed. Plastic pinch valves are not appropriate for these applications because they are generally limited to low positive pressure applications with tubing having 1/2 outer diameter and smaller. Metal pinch valves capable of providing the force needed are susceptible to corrosion, bulky and are far more expensive than the plastic valves. The metal pinch valves are less suitable for small tubing sizes and are not readily provided with calibration to allow repeatable valve settings.